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ISO 14879-1 Fatigue test of metallic tibial trays of total knee joint replacement system

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ISO 14879 - 1: Implants for Surgery — Total Knee Joint Replacements — Part 1: Static and Fatigue Testing of Tibial Trays

ISO 14879 - 1 is a core international standard formulated by the International Organization for Standardization (ISO) for the mechanical performance evaluation of metallic tibial trays in total knee replacements (TKR). As the first part of the ISO 14879 series, it specifies unified requirements for static mechanical testing and cyclic fatigue testing of tibial trays, serving as a globally recognized benchmark for medical device manufacturers, regulatory authorities, and testing institutions. Unlike region - specific standards such as ASTM F1800, this standard has wide applicability across international markets, providing a consistent technical basis for cross - border product certification and trade.

Core Scope and Purpose

Application Scope

  • It is specially applicable to metallic tibial trays used in total knee joint replacement systems, including both fixed - bearing and mobile - bearing design types.

  • The standard covers two major types of tests: static mechanical testing (to evaluate the ultimate load - bearing capacity and stiffness of the tibial tray) and cyclic fatigue testing (to simulate long - term physiological loading and assess durability).

  • It is not applicable to non - metallic tibial trays or tibial inserts (such as UHMWPE bearing components), which are covered by other supporting standards in the ISO 14879 series.

Core Objectives

  • Quantify the static mechanical properties (such as ultimate strength, bending stiffness) and fatigue durability of tibial trays to ensure they can withstand long - term physiological loads in the human body (such as walking, stair climbing, and squatting).

  • Unify test methods and technical indicators globally to eliminate technical barriers between different countries and regions and facilitate fair comparison of product performance.

  • Provide a standardized technical basis for the R&D, production quality control, and regulatory approval of tibial tray products, reducing the risk of clinical failure caused by mechanical performance defects.

    ISO 14879-1 Fatigue test of metallic tibial trays of total knee joint replacement system

Test Methods and Procedures

The standard divides the test into two core modules: static testing and fatigue testing, with strict specifications for test setup, loading parameters, and operation steps.

Sample Preparation

  • Sample Requirements: Test specimens must be finished products that fully conform to the formal production process, including material selection, machining, surface treatment, and sterilization (if applicable). The geometry, material composition, and mechanical properties must be consistent with clinical products.

  • Sample Quantity: To ensure statistical significance, a minimum of 5 specimens are required for each type of test (static or fatigue).

  • Fixation Method: Tibial trays are fixed using bone cement or high - strength epoxy resin in standardized metal test blocks. The fixation process must simulate the clinical implantation state to avoid abnormal stress concentration caused by improper fixation.

Static Testing

Static testing focuses on evaluating the tibial tray's ability to withstand extreme static loads and its deformation characteristics before failure.
  • Key Measurements: Record the load - displacement curve, and calculate indicators such as ultimate static load, yield strength, and static stiffness (slope of the linear elastic segment of the curve).

  • Failure Observation: Document the failure mode of the specimen, such as keel fracture, tray platform cracking, or plastic deformation of the bearing surface.

Fatigue Testing

Fatigue testing simulates the cyclic loading that tibial trays endure during long - term clinical use, which is the core part of the standard.


ParameterSpecificationRationale
Loading WaveformSinusoidal waveformSimulates the periodic mechanical load of the knee joint during daily activities
Load Ratio (R)0.1 (minimum load = 10% of maximum load)Maintains a stable compressive baseline to avoid damage caused by alternating tension - compression loads
Test Frequency5 - 10 HzBalances test efficiency and simulation accuracy, avoiding material heating due to excessive frequency
Cycle Count Requirement10 million cycles (minimum)Equivalent to 2 - 3 years of moderate activity for an average patient, covering the short - to medium - term service life of the implant
Peak LoadDetermined by the static test results, usually 30% - 50% of the ultimate static loadEnsures the test load is close to the actual physiological load level

Test Termination: The test stops when the specimen fractures, visible cracks appear, or the preset 10 million cycles are completed.


Related Supporting Standards

  • ISO 14879 - 2: The second part of the series, focusing on the testing requirements of tibial inserts (UHMWPE components).

  • ISO 7206 - 4: Specifies the static and fatigue testing methods for the overall knee joint prosthesis, which is complementary to ISO 14879 - 1.

  • ISO 10993: A series of standards for biological evaluation of medical devices, which is used in conjunction with ISO 14879 - 1 to complete the comprehensive evaluation of knee joint implants.


Acceptance and Fixtures


Test Fixtures and Apparatus

The standard has strict requirements for test fixtures to ensure that the load is applied accurately and the test state is consistent with the clinical scenario.

3.1 Core Fixture Components

Fixture ComponentFunctionDesign Requirements
Tibial Tray Fixing BlockFix the tibial tray to simulate in - vivo implantationMade of high - rigidity alloy steel, with a groove matching the keel of the tibial tray to ensure precise positioning
Load ApplicatorApply static or cyclic load to the trayEquipped with a spherical pressure head (covered with UHMWPE pads) to avoid local stress concentration and simulate the contact state between the femoral component and the tibial tray
Displacement and Force Measuring SystemCollect real - time load and displacement dataThe force sensor accuracy is not less than ±1% of the full - scale range, and the displacement measurement resolution is not less than 0.001 mm
Environmental Simulation Device (Optional)Simulate the in - vivo physiological environmentA constant - temperature water bath at 37°C ±2°C can be used to replicate the temperature and humidity of the human body


5.2 Comparison with Similar Standards (ASTM F1800)

AspectISO 14879 - 1ASTM F1800
ApplicabilityGlobal universal, adopted by most countries and regionsMainly used in the North American market
Test CycleMinimum 10 million cyclesMinimum 10 million cycles (consistent with ISO)
Loading Frequency5 - 10 Hz0.5 - 10 Hz (wider range)
Fixture DesignMore detailed requirements for the simulation of in - vivo fixation (such as bone cement usage)Focuses on the simplicity and repeatability of the fixture
Scope of ApplicationOnly for metallic tibial traysCovers metallic tibial trays of fixed - bearing knee systems


4. Key Parameters and Acceptance Criteria

ISO 14879 - 1 does not specify uniform mandatory performance thresholds (due to differences in tibial tray design, size, and material), but clearly defines acceptance evaluation criteria and data reporting requirements:
  • Static Performance: The tibial tray must not have catastrophic failure (such as sudden fracture) under the designed static load, and the ultimate load must be significantly higher than the maximum physiological load (usually 3 - 5 times the body weight).

  • Fatigue Performance: For specimens that complete 10 million cycles of testing, there must be no visible cracks, fractures, or excessive plastic deformation (the residual deformation shall not exceed 1% of the initial thickness of the tray).

  • Failure Judgment: If a specimen fails before reaching the specified number of cycles, the failure mode must be analyzed. If it is a design defect (rather than accidental damage), the product design needs to be optimized and re - tested.

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